Electrolytic barrel pickling and polishing



Dec. 4, 1945. s TOUR ET AL 2,390,282

ELECTROLYTIC BARREL PICKLING AND POLISHING Filed 0612. 19 1940 INVENTORS 5AM TOUR BY ALBERT HOWE 244w 'A ORNEY Patented nee. 4, 1945 mac'raon 'rrc mam. PICKLING AND rousnmc Sam Tour and Albert E. Howe, New York, N. Y., aseignors, by mesne assignments, to said Tour Application October 19, 1940, Serial No. 361,930

' 3 Claims. (cl. 204-140) The present invention relates to the electro treatment of metals, and has particular reference to anodic pickling and polishing.

It is the principal object of the invention to provide a practical anodic barrel treatment.

Another object of the invention is to provide a novel combination of electrolyte and metal for anodic barrel treatment.

A further object is to utilize a selected electrolyte and a selected anode to build up a passive anodic layer on the anode.

Still another object of the invention is to utilize a container without previously applied insulating coating for the anodic treatment of metals.

With the above and other objects and advantageous features in view, the invention consists of a novel method and novel combinations of electrolyte and metal anodes more fully disclosed in the detailed description following, and more specifically defined in the claims appended thereto.

The electrochemical treatment of work such as metal articles requires that electricalcontact be made with the articles being treated. For quantity treatment of small articles a barrel of nonconductive material, such as hard rubber or Bakelite, is used, and exposed metal contact points or strips are provided in the interior thereof. This type of arrangement may be used for electroplating, electropickling and electropoiishing.

In the case of electroplating, metal coats the contacts as well as the articles being plated; whereas in the case of electropolishing and electropickling, metal is removed from the articles being treated as well as from the contacts. Consequently, in the case of electropolishlng and electropickling, the contacts are continually being eaten away.

If the work is cathodic in the electrolyte, the passage of the current protects the contact points or strips from electrochemical attack; however, there has heretofore been no protection when the work is anodic, and the passage of current causes an electrochemical attack on the work being treated and on the exposed contact points 'and strips, which are rapidly eaten away.

Anodic pickling by the barrel method has not therefore been heretofore practical.

It'has been found that certain combinations of electrolytes and metal anodes eliminate the electrochemical attack and render anodic barrel pickling practicable. The electrolyte first being selected to suit the material of the articles bein metal for the contact points or strips or for the entire barrel.

If the metal-electrolyte combination selected utilizes a metal inert to the electrolyte, either with or without passage of the current, no attack on the metal will take place. Thus, platinum may be used in some cases, but it is found that current leaves the entire surface of the platinum whether or not' there is work to make con-. tact with, the entire surface area of the immersed platinum becoming effective anode area for the passage of current. If an entire barrel be constructed of platinum, the current loss becomes excessive, and the material cost for ordinary use prohibitive.

With certain combinations of electrolyte and metal, the immersed metal surface becomes passive on the application of the voltages used for anodic pickling or polishing and thus prevents excessive current loss from the exposed immersed surfaces and electrochemical dissolution of the metal used for contact points or strips or for the entire barrel.

Thus, aluminum used as an anode in electrolytes of sulphuric, chromlc, oxalic and other acids builds up passivity by formation of an anodic layer of considerable thickness, stability and permanence, the heavy anodic layer being a poor electrical conductor which prevents excess in loss of current from the exposed metal surfaces but which also prevents good electrical contact with the work to be treated.-

It is therefore preferred to use combinations of electrolyte and metal where the metal becomes passive and/or forms an anodic film, the passivity being readily broken by physical contact or impact of the metal articles being pickled or polished, or by mounting brushes, wheels, or the like to be contacted.

A preferred combination of electrolyte and metal suitable for electropolishing of stainless steel articles is an electrolyte of sulphuric and hydrofluoric acids together, in a barrel constructed ofpure copper. If a complete copper construction is adopted, the entire container is a contact point; although a passive coating forms on the copper surface with current flow, the slight impact of the tumbling work is sumcient to break through and establish contact.

Copper is easily workable and readily available, and has long life; while not completely passive, commercially pure copper will draw .005 amp/sq. in. if proper conditions are maintained, where stainless steel draws 3.5 amps/sq. in. The

treated, it is then necessary to select the pro er p ve condition is not as ood if pper alloy are used, or if the electrolyte is too low in sulphuricacid or is allowed to get too hot.

For stainless steel work 'such as nuts, bolts, screws, etc., the barrel ispreferably comparatively small and easy to handle, as the time factor is short and the required current density is high. It is not necessary to rinse the work rapidly, andloading and unloading without rinsing the acid oiT the barrel is feasible and will prevent introducing water into the electrolyte. Repeated tests have shown no evidence of any "burning in barrel treatment.

It is preferred to use a potential of 12 11020 volts, and as high a current density as necessary,

I the electrolyte.

Any type of" barrel may be used, one preferred form being an adaptation of the oblique plating barrel type, which permits frequent inspection of the work in process.

Another form preferred for the continuous treatment of small parts is of the totally submerged cylindrical barrel type, with a helical internal path. With the work passing through the solution in a thin layer, it is feasible to main- -tain anodic current densities of 5 to 10 amps/sq. in. and toreduce treatment time to a few minutes or fractions of a minute, .with good efliciency and performance.

In the appended drawingI have shown illustrative examples of equipment which can be employed in the practice of my invention. How-' ever, it is to be understood that equipment of other types can be employed, for the construction of the apparatus forms no part of the present invention.

Fig. 1 is a schematic sectional view of one form of electrolytic apparatus; and Fig. 2 is a longitudinal sectional view of one particular form of treating barrel which is preferred for the continuous treatment of small parts.

In the apparatus of Fig. 1, a tank I provided with a lead lining 2 contains an electrolyte 3. A perforate copper tumbling barrel 4 is obliquely arranged in the tank, as by means of a shaft 5, suitably supported. Heavy gauge woven copper mesh cathode elements 6 and 1 provide cathode surfaces inside and outside the barrel, being placed as close to the Work as possible. Frequent inspectionof the work may be had by tilting the barrel above the level of the electrolytic bath.

In the form of barrel shown in Fig. 2, the perforate shell 8 is provided with a helical element 9 affording a helical internal path for the parts lated from the barrel.

Other examples of electrolyte metal combinations suitable for the electropolishing of metals is the use of an electrolyte of sulphuric and phosphoric acids and-a barrel of copper. Copper alloys such as brass or nickel silver, zinc, cadmium or zinc cadmium alloys are also suitable forthe described use. Still another example of a suitable anode metal for electrolytes containing sulhuric acid is tantalum.

basic principles are described above are applicable to' electropickling and electropolishterials, but the difficulties caused by dissolution" of the metal are remedied according to the present invention by making the racks and baskets of a metal which becomes passive in the particular electrolyte used, the passivity being broken or removed, if desired, in any suitable manner.

Although specific combinations of electrolyte and metal have been disclosed which are suitable for anodic treatment, it is obvious that other combinations may be used, according to the work and to the electrolytic treatment and electrolyte most suitable therefor.

We claim:'

1. In an anodic electrolytic treatment of the class consisting of electropickling and electropolishing of metal articles in an electropolishing sulphuric acid-hydrofluoric acid-water electrolyte, the steps of immersing in said electrolyte a barrel electrode of copper, bringing the metal articles into contact with the inside surfaces of the barrel, making the barrel the anode while passing a current through the barrel, articles and electrolyte at a voltage and current density effective in said electrolytic treatment and under conditions which passivate the barrel with respect to the passage of current, and rotating the rel to establish electrical contact between the barrel and the articles.

2. In an anodic electrolytic treatment of the class consisting of 'electropick'ling and electropolishing of metal articles in an electropolishing electrolyt of the class consisting of sulphuric acid-hydrofluoric acid-water and sulphuric acidphosphoric acid-water, the steps of immersing in said electrolyte a barrel electrode of copper, bringing the metal articles into contact with the inside surfaces of the barrel, making the barrel the anode while passing a current through the barrel, articles and electrolyte at a voltage and current density effective in said electrolytic treatment and under conditions which passivate the barrel with respect to the passage of current, and rotating the barrel to produce relative movement and mechanical contact between the articles and barrel to establish electrical contact between the barrel and the articles.

3. In an anodic electrolytic treatment of the class consisting of electropickling and electropolishing of metal articles in an electropolishing sulphuric acid-phosphoric acid-water electrolyte, the steps of immersing in said electrolyte a barrel electrode of a metal of the class consisting of copper, brass, nickel silver, zinc, cadmium,--

alloys consisting essentially of zinc and cadmium, and tantalum, bringing the metal articles into contact with the inside surfaces of the barrel, making the barrel the anode while passing a current through th barrel, articles and electrolyte at a voltage and current density effective in said electrolytic treatment and under conditions which passivate the barrel with respect to the passage of current, and rotating the barrel to produce relative movement and mechanical contact between the articles and barrel to establish electrical contact between th barrel and the articles. SAM TOUR.

ALBERT E. HOWE. 

